1. Field of the Invention
The present invention is directed to circuit breakers for circuit protection and control of electrical distribution systems. It is suitable for application in low voltage alternating current electrical systems commonly employed in residential and commercial structures.
2. Description of the Prior Art
Circuit breakers are often mounted in electrical enclosures, such as metering stacks. Referring to FIG. 1, the metering enclosure 10 is of an exemplary type commonly used in multiple unit occupancy buildings. The enclosure 10 has a plurality of stacked electric meters 12 that are coupled to an electric power grid so that they can provide rate-metered electric power to each corresponding occupancy unit. In FIG. 1, each meter is in turn wired to a downstream circuit breaker 14, often through a metering socket assembly having a pair of male stabs that plug into female biased jaws incorporated into the circuit breaker (not shown). The circuit breaker 14 has a pair of load terminals, often of a terminal lug configuration. Each lug is wired to one or more load wires or cables 16. Generally circuit breaker load terminals are configured at the top of the circuit breaker 12, as shown in FIG. 1.
FIG. 2 shows a prior art two-pole circuit breaker 20 that is sold by Siemens Energy & Automation, Inc. The circuit breaker 20 has a left load lug 22 that employs an allen screw 24 for crimped capture of a load cable. There is also a right lug 26 with corresponding allen screw 28. Both lugs 22, 24 are retained in a molded breaker housing 30 proximal the top side housing wall 32. The front cover 34 includes windows 36, 38 for access to the allen screws 24, 28.
Referring back to FIG. 1, the load cables 16 are routed from the top of the circuit breaker 12 in a U-shaped bend and down in a meter enclosure gutter. Alternatively, the cables 16 are routed in an upwardly direction in an “S-bend”. The cables 16 thereafter exit the meter enclosure 10, for further distribution to the building occupancy units. Cable thickness dictates the U-bend or S-bend radius necessary for routing them from the circuit breaker to the gutter. As shown in FIG. 1, the cable 16 bend radius dictates minimum vertical spacing S between each meter 12 in the enclosure 10. It is desirable to minimize the vertical spacing S to maximize the number of meters that are stackable in an enclosure cabinet. Elimination of the need to form U-bends or S-bends in the load cables 16 is a desirable objective. One previous solution to eliminate the need for U-bend or S-bend formation in load cables was fabrication of a circuit breaker having side-access lugs.
FIG. 3 is a schematic representation of a left side-access circuit breaker 40 previously sold under the MURRAY® brand model designation 200V. The subject prior art circuit breaker 40 had a left lug 42 with allen screw 44 and a corresponding right lug 46 with allen screw 48. The circuit breaker housing 50 enabled left side access of load cables 16 along the left side wall 52. Front cover 54, along with upstanding internal walls 55 in the housing 50 captured and electrically isolated each respective breaker lug 42, 46. Windows 56, 58 enabled access to the allen screws 44, 46 for selective clamping of the load cables 16.
Full isolation of each of the lugs by surrounding insulating walls 55 and cover 54 was in compliance with electrical code over surface spacing requirements. For example, if a cable lug were not surrounded by insulating material on all sides with exception of the cable insertion direction, it might be possible to have excess cable protruding through the lug in violation of over surface spacing requirements. As a result of the over surface requirement, a drawback of the prior art breaker design 40 is that the lugs were configured at the factory for only left side load cable access, or in one other variation top access similar to the prior art circuit breaker of FIG. 2. If an electrical enclosure installation required right side cable routing rather than left side routing, the only practical recourse was to utilize a top-access circuit breaker.
It is desirable for electrical enclosure design an installation flexibility to eliminate the need for U-bend or S-bend cable clearances in applications that require left or right side cable gutter routing, or a combination of both in a single enclosure, while complying with electrical code over spacing requirements.